Hydrogen gas sensor utilizing electrically isolated tunneling magnetoresistive stress sensing elements

Abstract

A hydrogen gas sensor utilizing electrically isolated tunneling magnetoresistive stress sensing elements is disclosed. The hydrogen gas sensor comprises: a deformable substrate, a magnetoresistive bridge stress sensor located on the deformable substrate, an electrical isolation layer covering the magnetoresistive bridge stress sensor, a magnetic shielding layer located on the electrical isolation layer, and a hydrogen sensing layer located above the deformable substrate. The hydrogen sensing layer is located in a plane perpendicular to the deformation of the substrate covering the electrical isolation layer. The hydrogen sensing layer is used for absorbing or desorbing hydrogen gas to generate expansion or contraction deformation and cause a stress change of the deformable substrate. The magnetoresistive bridge stress sensor is used for measuring a hydrogen gas concentration utilizing the stress change of the deformable substrate. It results in a hydrogen gas sensor with improved performance.

The invention claimed is: 
     
       1. A hydrogen gas sensor utilizing electrically isolated tunneling magnetoresistive stress sensing elements, comprising:
 a deformable substrate; 
 a magnetoresistive bridge stress sensor located on the deformable substrate, an electrical isolation layer covering the magnetoresistive bridge stress sensor, and a magnetic shielding layer located on the electrical isolation layer; and 
 a hydrogen sensing layer located above the deformable substrate, where in the hydrogen sensing layer is located in a plane perpendicular to the deformation of the substrate covering the electrical isolation layer, the hydrogen sensing layer is configured to absorb or desorb hydrogen gas to generate expansion or contraction deformation and thus cause a stress change of the deformable substrate, and the magnetoresistive bridge stress sensor is configured to measure a hydrogen gas concentration utilizing the stress change of the deformable substrate. 
 
     
     
       2. The hydrogen gas sensor according to  claim 1 , wherein the deformable substrate is a cantilever beam; or,
 the deformable substrate is a membrane assembly; and the membrane assembly comprises a frame and a membrane enclosed in the frame, and the magnetoresistive bridge stress sensor is disposed on the membrane. 
 
     
     
       3. The hydrogen gas sensor according to  claim 2 , wherein the length direction of the deformable substrate is the X-axis direction, and the width direction of the deformable substrate is the Y-axis direction; and the magnetoresistive bridge stress sensor comprises a plurality of magnetoresistance sensor units, each of which comprises a multi-film layer stacked structure parallel to a plane X-Y, and the multi-film layer at least comprises a pinning layer, a reference layer, a barrier layer, a free layer, and a bias layer that are stacked in sequence. 
     
     
       4. The hydrogen gas sensor according to  claim 3 , wherein the deformable substrate has a first surface and a second surface which are arranged along the Z-axis direction;
 the magnetoresistive bridge stress sensor has a push-pull bridge structure, and comprises push magnetoresistance sensor units and pull magnetoresistance sensor units; 
 the push magnetoresistance sensor units are disposed on the first surface, and the pull magnetoresistance sensor units are disposed on the second surface; and the push magnetoresistance sensor units and the pull magnetoresistance sensor units bear stresses of the same magnitude and in the opposite directions. 
 
     
     
       5. The hydrogen gas sensor according to  claim 4 , wherein the angle at which the initial magnetic moment of the free layer of each push magnetoresistance sensor unit deviates from the Y-axis is α;
 when the magnetic moments of the free layers of the push magnetoresistance sensor units and the magnetic moments of the free layers of the pull magnetoresistance sensor units are simultaneously rotated clockwise or counterclockwise by the same angle to obtain the corresponding magnetic moments of the pinning layers, the angle at which the initial magnetic moment of the free layer of each pull magnetoresistance sensor unit deviates from the Y-axis is 90-α or 270-α; or, 
 when the magnetic moments of the free layers of the push magnetoresistance sensor units and the magnetic moments of the free layers of the pull magnetoresistance sensor units are rotated in different directions and by the same angle, the angle at which the initial magnetic moment of the free layer of each pull magnetoresistance sensor unit deviates from the Y-axis is 90+α or 270+α; and 
 the value range of α is from 0° to 360°, 
 wherein when the free layers are made of a material with a positive magnetostriction coefficient and bear a tensile stress or made of a material with a negative magnetostriction coefficient and bear a compressive stress, α is not 0° or 180°, and when the free layers are made of a material with a positive magnetostriction coefficient and bear a compressive stress or made of a material with a negative magnetostriction coefficient and bear a tensile stress, α is not 90° or 270°. 
 
     
     
       6. The hydrogen gas sensor according to  claim 3 , wherein the deformable substrate has a first surface and a second surface which are arranged along the Z-axis direction;
 the magnetoresistive bridge stress sensor has a push-pull bridge structure, and comprises push magnetoresistance sensor units and pull magnetoresistance sensor units; 
 the push magnetoresistance sensor units and the pull magnetoresistance sensor units are disposed on the first surface or the second surface at the same time; and the push magnetoresistance sensor units and the pull magnetoresistance sensor units bear stresses of the same magnitude and in the same direction. 
 
     
     
       7. The hydrogen gas sensor according to  claim 6 , wherein the angle at which the initial magnetic moment of the free layer of each push magnetoresistance sensor unit deviates from the Y-axis is α;
 when the magnetic moments of the free layers of the push magnetoresistance sensor units and the magnetic moments of the free layers of the pull magnetoresistance sensor units are simultaneously rotated clockwise or counterclockwise by 90° to obtain the corresponding magnetic moments of the pinning layers, the angle at which the initial magnetic moment of the free layer of each pull magnetoresistance sensor unit deviates from the Y-axis is 180-α or 360-α; or, 
 when the magnetic moments of the free layers of the push magnetoresistance sensor units and the magnetic moments of the free layers of the pull magnetoresistance sensor units are rotated in different directions and by the same angle, the angle at which the initial magnetic moment of the free layer of each pull magnetoresistance sensor unit deviates from the Y-axis is α or 180+α; and 
 the value range of α is from 0° to 360°, 
 wherein when the free layers are made of a material with a positive magnetostriction coefficient and bear a tensile stress or made of a material with a negative magnetostriction coefficient and bear a compressive stress, α is not 0° or 180°, and when the free layers are made of a material with a positive magnetostriction coefficient and bear a compressive stress or made of a material with a negative magnetostriction coefficient and bear a tensile stress, α is not 90° or 270°. 
 
     
     
       8. The hydrogen gas sensor according to  claim 3 , further comprising: a non-hydrogen sensing layer in the same layer as the hydrogen sensing layer; wherein
 the cantilever beam comprises a fixed part and a reference cantilever beam and a sensing cantilever beam which are respectively disposed at the two sides of the fixed part, the reference cantilever beam is provided with a reference area, and the sensing cantilever beam is provided with a sensing area; or, 
 the membrane assembly comprises a reference membrane and a sensing membrane which are enclosed in the frame, the reference membrane is provided with a reference area, and the sensing membrane is provided with a sensing area; and 
 the hydrogen sensing layer is disposed on the magnetic shielding layer within the sensing area, and the non-hydrogen sensing layer is disposed on the magnetic shielding layer within the reference area. 
 
     
     
       9. The hydrogen gas sensor according to  claim 8 , wherein
 the reference area and the sensing area of the deformable substrate are located on the same plane; 
 the magnetoresistive bridge stress sensor has a reference bridge structure, and comprises reference magnetoresistance sensor units and sensing magnetoresistance sensor units; and 
 the reference magnetoresistance sensor units are disposed in the reference area, and the sensing magnetoresistance sensor units are disposed in the sensing area. 
 
     
     
       10. The hydrogen gas sensor according to  claim 9 , wherein the angle at which the initial magnetic moment of the free layer of each reference magnetoresistance sensor unit deviates from the Y-axis is α, and the angle at which the initial magnetic moment of the free layer of each sensing magnetoresistance sensor unit deviates from the Y-axis is α;
 the magnetic moments of the free layers of the reference magnetoresistance sensor units and the magnetic moments of the free layers of the sensing magnetoresistance sensor units are simultaneously rotated clockwise or counterclockwise by the same angle to obtain the corresponding magnetic moments of the pinning layers; and 
 the value range of α is from 0° to 360°, 
 wherein when the free layers are made of a material with a positive magnetostriction coefficient and bear a tensile stress or made of a material with a negative magnetostriction coefficient and bear a compressive stress, α is not 0° or 180°, and when the free layers are made of a material with a positive magnetostriction coefficient and bear a compressive stress or made of a material with a negative magnetostriction coefficient and bear a tensile stress, α is not 90° or 270°. 
 
     
     
       11. The hydrogen gas sensor according to  claim 1 , wherein the magnetoresistive bridge stress sensor is provided with an electrical transmission port assembly, and the electrical transmission port assembly is directly connected with the deformable substrate and is sealed on the deformable substrate by means of sealant. 
     
     
       12. The hydrogen gas sensor according to  claim 1 , wherein the hydrogen sensing layer comprises at least one of AB 5 , AB 3 , AB 2 , AB, and A 2 B type intermetallic compounds, A represents a strong metal hydride forming element, and B represents a transition metal element. 
     
     
       13. The hydrogen gas sensor according to  claim 12 , wherein the A can be rare earth metals, Ca, Mg, Zr, or Ti, and the B can be Ni, Co, Fe, Mn, or Cr.